/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

package com.sun.mail.imap.protocol;

import java.text.StringCharacterIterator;
import java.text.CharacterIterator;

/**
 * See the BASE64MailboxEncoder for a description of the RFC2060 and how
 * mailbox names should be encoded. This class will do the correct decoding
 * for mailbox names.
 * 
 * @author Christopher Cotton
 */

public class BASE64MailboxDecoder {

	public static String decode(String original) {
		if (original == null || original.length() == 0)
			return original;

		boolean changedString = false;
		int copyTo = 0;
		// it will always be less than the original
		char[] chars = new char[original.length()];
		StringCharacterIterator iter = new StringCharacterIterator(original);

		for (char c = iter.first(); c != CharacterIterator.DONE; c = iter.next()) {

			if (c == '&') {
				changedString = true;
				copyTo = base64decode(chars, copyTo, iter);
			} else {
				chars[copyTo++] = c;
			}
		}

		// now create our string from the char array
		if (changedString) {
			return new String(chars, 0, copyTo);
		} else {
			return original;
		}
	}

	protected static int base64decode(char[] buffer, int offset, CharacterIterator iter) {
		boolean firsttime = true;
		int leftover = -1;

		while (true) {
			// get the first byte
			byte orig_0 = (byte) iter.next();
			if (orig_0 == -1)
				break; // no more chars
			if (orig_0 == '-') {
				if (firsttime) {
					// means we got the string "&-" which is turned into a "&"
					buffer[offset++] = '&';
				}
				// we are done now
				break;
			}
			firsttime = false;

			// next byte
			byte orig_1 = (byte) iter.next();
			if (orig_1 == -1 || orig_1 == '-')
				break; // no more chars, invalid base64

			byte a, b, current;
			a = pem_convert_array[orig_0 & 0xff];
			b = pem_convert_array[orig_1 & 0xff];
			// The first decoded byte
			current = (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3));

			// use the leftover to create a Unicode Character (2 bytes)
			if (leftover != -1) {
				buffer[offset++] = (char) (leftover << 8 | (current & 0xff));
				leftover = -1;
			} else {
				leftover = current & 0xff;
			}

			byte orig_2 = (byte) iter.next();
			if (orig_2 == '=') { // End of this BASE64 encoding
				continue;
			} else if (orig_2 == -1 || orig_2 == '-') {
				break; // no more chars
			}

			// second decoded byte
			a = b;
			b = pem_convert_array[orig_2 & 0xff];
			current = (byte) (((a << 4) & 0xf0) | ((b >>> 2) & 0xf));

			// use the leftover to create a Unicode Character (2 bytes)
			if (leftover != -1) {
				buffer[offset++] = (char) (leftover << 8 | (current & 0xff));
				leftover = -1;
			} else {
				leftover = current & 0xff;
			}

			byte orig_3 = (byte) iter.next();
			if (orig_3 == '=') { // End of this BASE64 encoding
				continue;
			} else if (orig_3 == -1 || orig_3 == '-') {
				break; // no more chars
			}

			// The third decoded byte
			a = b;
			b = pem_convert_array[orig_3 & 0xff];
			current = (byte) (((a << 6) & 0xc0) | (b & 0x3f));

			// use the leftover to create a Unicode Character (2 bytes)
			if (leftover != -1) {
				buffer[offset++] = (char) (leftover << 8 | (current & 0xff));
				leftover = -1;
			} else {
				leftover = current & 0xff;
			}
		}

		return offset;
	}

	/**
	 * This character array provides the character to value map
	 * based on RFC1521, but with the modification from RFC2060
	 * which changes the '/' to a ','.
	 */

	// shared with BASE64MailboxEncoder
	static final char pem_array[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
	'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
	'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
	'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
	'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
	'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
	'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
	'4', '5', '6', '7', '8', '9', '+', ',' // 7
	};

	private static final byte pem_convert_array[] = new byte[256];

	static {
		for (int i = 0; i < 255; i++)
			pem_convert_array[i] = -1;
		for (int i = 0; i < pem_array.length; i++)
			pem_convert_array[pem_array[i]] = (byte) i;
	}
}
